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6.1.13

£1 Lithium Ion Battery Charger

One cheap PCB from an auction site. 1 scrap bit of copper pipe. 2 bronze pennies. Put them together and charge up a 18650 Li ion cell.

If like me you have a stash of rechargeable 18650 Lithium ion cells (perhaps from a defunct laptop battery) but no battery holders, here's how to make your own. First remove the spring terminals from a dead lantern battery using aviation snips.

Find a scrap bit of copper pipe 22 mm OD (approximately 3/4" ID). Trim it to the combined length of the battery and terminal and then cut in half lengthways using a hacksaw. Each halfpipe will make one battery holder.

British 1p coins have exactly the right diameter to fit inside the halfpipe. Pre-1992 pennies are best because they are made of solid bronze instead of copper clad steel. Make a big hole in one of the pennies to feed through the connection from the spring terminal. Make a small hole near the edge of the other penny to attach a copper wire.

Clamp the drilled pennies to the halfpipe using hose clips and solder them in place using acid flux and a propane torch. An easy way to clean up the copper after soldering is to place in a mug with a scrunched up ball of aluminium foil, add a heaped tablespoon of bicarbonate of soda, top up with boiling water, and leave to soak for 15 minutes.

Solder a black wire to the spring terminal (negative) and a red wire to the penny at the other end (the positive terminal). Put a big round solder blob in the middle of the positive terminal to improve the connection to the cell and facilitate removal. There are your battery holders. Easy!

To make a battery charger, just solder the red and black leads to the BATT+/- terminals on the charger board. I got this PCB on eBay for US $1.58 (£0.98). It can be powered by a mini USB cable and features a TP4056 chip which is a generic version of the LTC4056 Li ion charger chip.

Just so you know, your 18650 is probably crap. It's marked 3800mAh. 3800mAh 18650s don't exist. The biggest capacity cell currently made is the 3400mAh NCR18650B by Panasonic. Anything claiming a bigger capacity is lying.